The present invention relates to white sidewall tires and a method for their manufacture, and more particularly to white sidewall tires of the radial-ply type.
In the known procedures for applying a decorative annular white band or strip on the outer-facing sidewall area of a tire whose reinforcing carcass structure is of the bias-ply type, the tire is built up with appropriate reinforcing plies, and elastomer covering strips are used to form sidewall and tread areas. At a preselected annular area on the sidewall, pigmented white elastomer is arranged which is overlayed with black elastomer. Typically, the pigmented white elastomer and black elastomer are preformed (e.g., by extrusion) as a composite strip which can be generally annularly arranged about the sidewall in one or a number of pieces, and most typically the preforming is of a sandwich-type composite comprised of black elastomeric base, overlaying white pigmented elastomer and overlaying black elastomer. The white pigmented portion of the composite (indeed the entire composite) generally is substantially wider than the eventual intended white sidewall strip in the finished tire.
The tire built up in this fashion is cured or vulcanized, with the result that the composite annular strip becomes an integral part of the sidewall of the tire, and the mold in which the tire is cured is configured so as to result in a portion of the composite strip being raised above the surface of the neighboring sidewall areas. The tire is then mounted on a rotating device so as to be outer-facing, and cutting blades are then arranged at the sidewall area where the composite strip exists. Opposed cutting blades are spaced apart a predetermined distance so as to define the width of the desired decorative white sidewall area and adjusted to achieve a cutting depth which will expose the white pigmented portion of the sidewall. As the tire rotates in contact with the blades, an annular ring consisting of covering black rubber and a small portion of underlying white rubber is removed, leaving in the sidewall area a decorative, defined, annular white ring recessed from the tire sidewall surface, i.e., in the nature of a groove. Owing to the recessed nature of the white sidewall area, the white sidewall generally is found to resist scuffing or dirtying as tires are stacked one upon the other or one next to the other for transportation, storage, and the like.
As the art and consumers moved progressively to wide-scale acceptance of tires of the radial-ply rather than bias-ply type, it became apparent that the known methods for providing decorative white sidewalls on bias-ply tires could not be employed for radial tire designs. In particular, it was unacceptable to cut into the sidewall area to expose a recessed area of the white rubber, for to do so would introduce a potential failure point in the tire inasmuch as the tire is deliberately constructed to flex radially.
In providing decorative white sidewalls on radial tires, then, the art developed a procedure wherein a composite strip of white elastomer covered by a thin black elastomer veneer (and generally overlaying a black elastomeric base as in the sandwichtype arrangement previously discussed) is arranged generally annularly about the sidewall area. Upon curing in a suitable mold, the composite becomes integrally associated with the sidewall area and the mold configuration is such that a predetermined width of the annular composite, eventually defining the general white sidewall width, is slightly raised above the surface of the surrounding sidewall areas. In the next step, the tire is mounted, outer-facing, on a rotating device and one or more circular buffing stones, rotating in a plane generally perpendicular to the plane of rotation of the tire, and whose buffing surfaces are at least as wide as the predetermined width of the protruding sidewall area, are placed in contact with the raised sidewall strip. As the tire and stones rotate in their respective planes, the thin black rubber veneer covering the underlying white rubber is buffed off to expose an annular decorative white sidewall strip. Generally, the surface of the buffing stone is flat or even slightly concave such that the cross-sectional shape of the exposed surface of the white sidewall strip is either flat or slightly convex. In the finished form, the white sidewall strip remains slightly raised above the surrounding sidewall surface, a necessary requirement in order to attain a clearly and sharply defined white sidewall.
As a consequence of the process required for providing white sidewalls on radial tires, i.e., resulting in a raised annular white area, it is found that the white sidewalls are quite prone to scuffing and dirtying in the normal course of, e.g., transportation and storage of the tires. While removable protective covers or removable pigmented protective solutions can be applied to the whitewall strip, this introduces yet another step in the overall process and detracts, at least until removed, from the aesthetic effect sought to be obtained from the whitewall.